Voltage overload arrester

ABSTRACT

A voltage overload arrester comprising a pair of shaped electrodes having surface portions in spaced adjacent relation to each other and gas tightly sealed in an insulating housing. The adjacent surface portions of each electrode are provided with a thin coating of a sintered mixture of a material having a high thermal electron-emission ability and including Ni, a mixture of Ni and ThO2 and a mixture of Ni, MgO and ThO2.

United States Patent Bahr et al.

[151 3,691,428 51 Sept. 12,1972

[54] VOLTAGE OYERLOAD ARRESTER [72] Inventors: Alex Bahr; Gerhard Peche, both of Berlin, Germany [73] Assignee: Siemens Aktiengesellschaft [22] Filed: July 13, 1970 [21] Appl. No.: 54,312

[30] Foreign Application Priority Data July 14, 1969 Germany ..P 19 35 734.7

[52] US. Cl. ..317/61, 313/218, 317/70 [51] Int. Cl. ..H02h 1/04 [58] Field of Search ..317/70, 61; 315/36; 313/218 [56] References Cited UNITED STATES PATENTS Kott 313/218 x 3,286,119 11/1966 Sugawara et al ..313/218 X 3,530,327 9/1970 Zollweg et al. ..313/218 X 3,349,276 10/1967 Jacobs et a1. ..313/218 X 3,535,582 10/1970 Kawiecki ..317/70 X Primary Examiner-James D. Trammell Attorney-Hill, Sherman, Meroni, Gross & Simpson [5 7] ABSTRACT A voltage overload arrester comprising a pair of shaped electrodes having surface portions in spaced adjacent relation to each other and gas tightly sealed in an insulating housing. The adjacent surface portions of each electrode are provided with a thin coating of a sintered mixture of a material having a high thermal electron-emission ability and including Ni, a mixture of Ni and ThO and a mixture of Ni, MgO and Th0,.

10 Claims, 1 Drawing Figure PATENTEU I973 3.691.428

HWENTORS fl/ex Bah)" erfiard ea/7e V ATTYS.

1 VOLTAGE OVERLOAD ARRESTER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a voltage overload protection device, and more particularly to a voltage overload arrester having electron-emission materials therein.

2. Prior Art German Pat. No. 615,506 teaches a voltage overload arrester device wherein the work surfaces of the electrodes are positioned adjacent to each other within the device and are provided with an additional layer of a further material. This material apparently functions to lower the work function of the electrodes and allows the electrodes to function as a cathode, i.e., an electron-emission device. Such electron-emission device in an overload arrester functions to lower the voltage drop and the power loss during periods of overloading current.

The capacitance of a voltage overload arrester essentially depends on the glowing or arc-burning voltage, the arc-passing current and on the cross sectional dimension of the electrode surface as well as the power supply lines. Of course, the cross sectional dimension is limited by the actual size of an overload arrester. However, an increase in the field electron-emission at the electrode surfaces, which function as a cathode (sometimes referred to herein as a cold arc cathode) would materially increase a capacitance of an overload arrester.

Prior art suggests that any layer or the like positioned on top of a work surface of an electrode must be maintained as this as possible. A thin layer provides a relatively small transfer resistance in the layer so that no noticeable power loss is produced. Of course, a power loss lowers the capacitance of a voltage overload arrester and is to be avoided. However, thin layers in an overload arrester are easily damaged and/or destroyed during overload period. Thus, the prior art devices utilizing a layer of matcrial, on the work surface of the electrode has a necessarily short working life limited by the thickness of the layer on the work surface.

SUMMARY OF THE INVENTION The invention provides a means of increasing the working life of such voltage overload arresters. ln accordance with the principles of the invention, the work surfaces of electrodes in a voltage overload arrester are provided with a sintered coating having a high thermal electron-emission ability. The coating is provided as a powdered mixture of grains of various components and sintered at about 900 C. onto the electrode work surfaces so as to form a tightly adhering coating. The components utilized to form the sintered coating includes a material having a relatively high electron-emission ability (such as rare earth metals) mixed with Ni, mixtures of Ni and Th0, and mixtures of Ni, Th0, and MgO.

The drawing illustrates, in an elevated diagrammatic cross sectional view, an example of a voltage overload arrester constructed in accordance with the principles of the invention.

The components of the sintered mixture impart extremely desirable features to the sinter formed layer on the work surfaces of the electrodes in a voltage overload arrester. A particularly desirable feature consists of the fact that the presence of nickel materially reduces the bulk or mass of a semi-conductor) of the sintered layer. Another desirable feature consists of the fact that the presence of magnesium oxide materially lowers the magnitude of the arc-passing current. A further feature consists of the fact that the presence of a material having a high thermal electron-emission ability, such as various rare earths and preferable thorium oxide, increases the field electron-emission ability of the work surfaces. Nickel also provides an improved adhesive quality.

The useful working life of a voltage overload arrester constructed in accordance as principles of the invention is materially increased by the significant lowering of the arc-passing current. The apparent reason for the increased working life is related to the fact that spattering (or sputtering) of the cathode surface is not as vigorous (i.e., is smaller) with an arc discharge in the overload arrester as compared with a glow discharge therein.

Referring now to the sample embodiment illustrated in the drawings, a voltage overload arrester 10 is provided with a somewhat tubularly shaped insulating body 1. A pair of generally frustum-shaped electrodes 2 and 3 are positioned within the body 1 and sealed therein by gas-tight seal means (not shown). The electrodes 2 and 3 are positioned so that their respective work or frontal surfaces 20 and 3a, respectively, are positioned to face each other in a spaced adjacent relation.

Preferably, the insulating body 1 is composed of glass or a ceramic material. The electrodes are preferably composed of a nickel-iron alloy or a nickel-iron-cobalt alloy.

It will be noted that the electrodes 2 and 3 have end portions protruding beyond the confines of the insulating body 1 so as to define contact terminals for connection with a particular electrical circuit wherein the safety of the voltage overload arrester is desired. As indicated before, the arrester 10 is formed to be gas-impermeable so that interior thereof may be substantially completely evacuated or filled with an inert or noble gas as desired.

A relatively thin layer 4 is provided on the adjacent work surfaces 2a and 3a, respectively. The layer 4 is sintered onto each of the surfaces 2a and 3a at temperatures of about 900 C. to form a tightly adhering outer peripheral coating or layer on such surfaces. Preferably, the layer 4 is composed of a material having a relatively high thermal electron-emission ability and includes at least nickel or a nickel-thorium oxide mixture and/or a nickel-magnesium oxide and thorium oxide mixture. Of course, only one of the surfaces 2a or 3a has to be so coated to provide a functional overload arrester.

The material of the layer 4 is provided as a uniformly powdered grain mixture, which mixture is placed in a suitably volatile binder, spread in a desired thickness on the surfaces 2a and 3a and then subjected to sintering conditions sufi'icient to produce a tightly adhering layer on their respective surfaces.

Preferably, the amount of nickel present in the sintered layer 4 ranges from about 30 percent to percent the amount of thorium oxide ranges from 10 percent to 50 percent and the amount of magnesium oxide ranges from percent to about 20 percent, all percentages being by weight. Thus, it will be noted that in some embodiments of the invention only nickel and a material having a high thermal electron-emission ability are present. While in other embodiments only nickel and thorium oxide are present, still in others, magnesium oxide and thorium oxide are all present. The preferred grain size of thorium oxide particles ranges from about 1 pm to 50 pm, the grain size of the nickel particles range from about 1 pm to 50 um, while the grain size of the magnesium oxide particles range from about 0.2 pm to 10 pm. An exceptionally useful grain size for thorium oxide is 30 am, for nickel 10 um and for magnesium oxide 2 pm.

While thorium oxide is the preferred material for use as an electron-emission material at high thermal condition, other rare earth metals are also suitable.

Various modifications or changes may be effected to the exemplary embodiments described without departing from the spirit and scope of the invention.

We claim as our invention:

1. A voltage overload arrester comprising, a gas-tight housing, a pair of shaped electrode members positioned in working relation within the housing, said electrodes each having a work surface in spaced facing relation to each other, and an outer peripheral layer composed of a mixture of a material having a relatively high thermal electron-emission ability and at least nickel sintered onto at least one of the electrode work surfaces.

2. A voltage overload arrester as defined in claim 1 wherein the outer peripheral layer includes magnesium oxide as a component.

3. A voltage overload arrester as defined in claim 2 wherein the outer peripheral layer is composed of a mixture including about 30 percent to 90 percent by weight of nickel, and up to about 20 percent by weight of magnesium oxide.

4. A voltage overload arrester as defined in claim 1 wherein the material having a relatively high thermal electron-emission ability in the outer peripheral layer is thorium oxide.

5. A voltage overload arrester comprising, a gas-fight housing, a pair of shaped electrode members positioned in working relation within the housing, said electrodes each having a work surface in spaced facing relation to each other, and an outer peripheral layer composed of a substantially uniform mixture of a material consisting essentially of 10 percent to 50 percent by weight of thorium oxide, 30 percent to 90 percent by weight nickel and 0 percent to 20 percent by weight magnesium oxide sintered onto at least one of the electrode work surfaces.

6. A voltage overload arrester as defined in claim 5 wherein the material of the mixture is in a powdered form and the thorium oxide powder has an average grain size ranging from about 1 pm to about 50 pm, the nickel powder has an average grain size ranging from about 1 pm to 50 um, and the magnesium oxide powder has an average grain size ranging from about 0.2 pm to about 10 pm.

7. A voltage arrester as defined in claim 5 wherein the material of the mixture is in a powdered form and the thorium oxide powder has an average grain size of about 30 pm the nickel wder has an average grain srze of about l0 um and e magnesium powder has an average grain size of about 2 pm.

8. A voltage overload arrester comprising, a housing composed of an insulating material having a pair of openings formed therein, electrodes extending through the openings of said housing and positioned adjacently spaced from one and her and having work surfaces in spaced facing relation to each other, a means sealing said electrodes to said housing to form a gas-impermeable housing, said electrodes protruding beyond said means to form contact points, and an outer peripheral layer sintered onto at least one of said work surfaces, said layer being composed of a mixture of a material having a relatively high thermal electron-emission ability selected from the group consisting essentially of a rare earth metal and thorium oxide, and another material including at least nickel said materials being a powder having an average grain size below about 50 m.

9. A voltage overload arrester as defined in claim 8 wherein the outer peripheral layer is composed of a substantially uniform mixture containing about 10 percent to 50 percent by weight thorium oxide, 30 percent to percent by weight nickel and up to 20 percent by weight magnesium oxide.

10. A voltage overload arrester as defined in claim 8 wherein the outer peripheral layer is composed of a substantially uniform mixture containing about 10 percent to 50 percent by weight of thorium oxide powder having an average grain size of about 30 percent am, about 30 percent to 90 percent by weight of nickel powder having an average grain size of about 10 um and up to about 20 percent by weight of magnesium oxide powder having an average grain size of about 2 pm. 

2. A voltage overload arrester as defined in claim 1 wherein the outer peripheral layer includes magnesium oxide as a component.
 3. A voltage overload arrester as defined in claim 2 wherein the outer peripheral layer is composed of a mixture including about 30 percent to 90 percent by weight of nickel, and up to about 20 percent by weight of magnesium oxide.
 4. A voltage overload arrester as defined in claim 1 wherein the material having a relatively high thermal electron-emission ability in the outer peripheral layer is thorium oxide.
 5. A voltage overload arrester comprising, a gas-tight housing, a pair of shaped electrode members positioned in working relation within the housing, said electrodes each having a work surface in spaced facing relation to each other, and an outer peripheral layer composed of a substantially uniform mixture of a material consisting essentially of 10 percent to 50 percent by weight of thorium oxide, 30 percent to 90 percent by weight nickel and 0 percent to 20 percent by weight magnesium oxide sintered onto at least one of the electrode work surfaces.
 6. A voltage overload arrester as defined in claim 5 wherein the material of the mixture is in a powdered form and the thorium oxide powder has an average grain size ranging from about 1 Mu m to about 50 Mu m, the nickel powder has an average grain size ranging from about 1 Mu m to 50 Mu m, and the magnesium oxide powder has an average grain size ranging from about 0.2 Mu m to about 10 Mu m.
 7. A voltage arrester as defined in claim 5 wherein the material of the mixture is in a powdered form and the thorium oxide powder has an average grain size of about 30 Mu m, the nickel powder has an average grain size of about 10 Mu m and the magnesium powder has an average grain size of about 2 Mu m.
 8. A voltage overload arrester comprising, a housing composed of an insulating material having a pair of openings formed therein, electrodes extending through the openings of said housing and positioned adjacently spaced from one and her and having work surfaces in spaced facing relation to each other, a means sealing said electrodes to said housing to form a gas-impermeable housing, said electrodes protruding beyond said means to form contact points, and an outer peripheral layer sintered onto at least one of said work surfaces, said layer being composed of a mixture of a material having a relatively high thermal electron-emission ability selected from the group consisting essentially of a rare earth metal and thorium oxide, and another material including at least nickel said materials being a powder having an average grain size below abouT 50 m.
 9. A voltage overload arrester as defined in claim 8 wherein the outer peripheral layer is composed of a substantially uniform mixture containing about 10 percent to 50 percent by weight thorium oxide, 30 percent to 90 percent by weight nickel and up to 20 percent by weight magnesium oxide.
 10. A voltage overload arrester as defined in claim 8 wherein the outer peripheral layer is composed of a substantially uniform mixture containing about 10 percent to 50 percent by weight of thorium oxide powder having an average grain size of about 30 percent Mu m, about 30 percent to 90 percent by weight of nickel powder having an average grain size of about 10 Mu m and up to about 20 percent by weight of magnesium oxide powder having an average grain size of about 2 Mu m. 